🚀 go-pugleaf

In article <JPOLITO.92Dec9155725@sysgem1.encore.com> jpolito@sysgem1.encore.com (Jonathan Polito) writes:

> I am curious to what the current wisdom is on accepting char* as a
> valid argument to a function expecting const char*&

It's invalid, though the reason may not be obvious at first glance.

The main thing to realize is that const char*& means "reference to
pointer to const char" and not "reference to constant pointer to
char" as one might think at first.

That means that in order to accept a char* as an argument, it would
be necessary to convert the char* to a temporary of type const char*
and then bind a reference to that temporary.  However, the reference
does not refer to a const object (because a pointer to const is not
itself a const), so it must be bound to a variable of the same type and
not a temporary.

The thing that makes this example tricky is that if we define

	typedef char* T;

then const T and const char* represent different types! -- const T is
"constant pointer to char" and const char* is "pointer to constant char".

The way to write "constant pointer to char" without a typedef it
char *const&, so the following should be OK:

	extern void f(char *const&);

	main()
	{
		char* p = /* some value */;
		f(p);
		// ...
	}

Here, p is of type "pointer to char" and there is no problem binding to
p a "reference to constant pointer to char".
-- 
				--Andrew Koenig
				  ark@europa.att.com